Voltage divider calculator
Output voltage, output impedance, and standing current — plus reverse mode: find R2 for a target output.
The circuit this computes
Voltage Divider — fully explained →How it works
Two resistors in series share the input voltage in proportion to their resistance: Vout = Vin · R2 / (R1 + R2). The same current flows through both, so the bigger resistor takes the bigger share of the voltage.
The two numbers everyone forgets: the output impedance (R1 ∥ R2 — what a load actually sees), and the standing current (Vin / (R1+R2)) that flows forever, which matters on batteries.
Common questions
Almost never. A divider makes a reference voltage, not a supply: any load current flows through R1 and drags the output down. The output impedance line in this calculator (R1 ∥ R2) tells you how badly — a load comparable to that impedance sags the output significantly. To power things, use a regulator.
It's the RATIO that sets the voltage; the absolute values set the standing current and the stiffness. 10k–100k total is the usual sweet spot: small enough to drive an ADC pin, large enough not to waste battery. The calculator shows the always-flowing current so you can judge.
The thing you connected is now part of the divider — its input resistance sits in parallel with R2. If the load is less than ~10× the divider's output impedance, the error is over a percent and grows fast. Buffer with an op-amp follower when it matters.